The control of gold nanoparticlesï¿½ surface chemistry is a fundamental prerequisite to tailor their properties for biological applications such as bioimaging and sensing. Short peptides have been specifically designed to form self-assembled monolayers on gold nanoparticles surface1,2 and used to increase their stability3 and enable functionalization with biomolecule at a stoichiometric level.2,4 Here, we propose an experimental and computational approach to characterize the molecular organization and define the secondary structure of self-assembled monolayers of peptides on gold nanoparticles surface. Experimentally, we are focusing on the benzophenone-derivative peptides, aiming to characterize the organization of mixed ligand shells on the gold nanoparticles surface. Under excitation at 350 nm, the carbonyl group of the benzophenone moiety crosslinks to an adjacent molecule. The cross-linking between the two adjacent ligands on the surface of the nanoparticles is monitored by Fourier Transform Infrared (FTIR), Ultraviolet-Visible (UV-Vis) spectroscopies and Mass Spectrometry (MS), providing insight into the molecular organization and structural response of these ligand shells upon light irradiation. We are using Molecular Dynamics simulations to investigate the secondary structure of two short peptides, i.e. CALNN and CFGAILSS, on spherical GNPs of different sizes, i.e. 5, 10, 25 nm. The model is validated on the basis of Shaw et al. work5 where they have shown, using a combination of Fourier Transform Infrared (FTIR) spectroscopy and Solid-State Nuclear Magnetic Resonance (SSNMR), that the CFGAILSSï¿½ conformation on the gold nanoparticles surface depends on the size of the particle, hence on its curvature. Both these approaches are necessary in order to have an insight at the molecular level into the organization and structure of self-assembled monolayers of peptides coating the gold nanoparticles surface. References: 1. Lï¿½vy, R. et al. Rational and combinatorial design of peptide capping ligands for gold nanoparticles. J. Am. Chem. Soc. 126, 10076ï¿½84 (2004). 2. Duchesne, L., Gentili, D., Comes-Franchini, M. & Fernig, D. G. Robust Ligand Shells for Biological Applications of Gold Nanoparticles. Langmuir 24, 13572ï¿½13580 (2008). 3. Chen, X. Y. et al. Features of Thiolated Ligands Promoting Resistance to Ligand Exchange in Self-Assembled Monolayers on Gold Nanoparticles. Aust. J. Chem. 65, 266ï¿½274 (2012). 4. Duchesne, L. et al. Transport of fibroblast growth factor 2 in the pericellular matrix is controlled by the spatial distribution of its binding sites in heparan sulfate. PLoS Biol. 10, 16 (2012). 5. Shaw, C. P., Middleton, D. a, Volk, M. & Lï¿½vy, R. Amyloid-derived peptide forms self-assembled monolayers on gold nanoparticle with a curvature-dependent ?-sheet structure. ACS Nano 6, 1416ï¿½26 (2012)